(Representing BESIII Collaboration) Institute of High Energy Physics, Beijing. QCD10, June 28 July 3, 2010, Montpellier, France

Transcription

1 BESIII status and results Xiaoyan SHEN (Representing BESIII Collaboration) Institute of High Energy Physics, Beijing 0 QCD10, June 28 July 3, 2010, Montpellier, France

2 Introduction Status of BESIII Outline Recent results from BESIII Summary

3 Beijing Electron Positron Collider (BEPC) at IHEP BES Storage ring Linac BSRF 3

4 (BEPC/BES) beam energy: GeV Physics goal BES The Y s are here! transition region between pqcd and non pqcd. 4 4

5 nsn2.5m8bepcii Storage Ring: Double ring RF 2 mrad822 SR RF 1..1Beam energy: GeV Luminosity: cm -2 s -1 O energy: 1.89 GeV 0.Optimum Energy spread: c5cm No. of bunches: 93 mbunch length: 1.5 cm Total current: 0.91 A SR mode: 2.5 GeV IP

6 BESIII Magnet: 1 T Super conducting MDC: small cell & Gas: He/C3H8 (60/40), 43 layers σ xy =130 μm σ p /p = de/dx=6% TOF: σ T = 100 ps Barrel 110 ps Endcap EMC: CsI crystal, 28 cm ΔE/E = GeV σz = 0.6 cm/ E Data Acquisition: Event rate = 4 khz Total data volume ~ 50 MB/s Muon ID: 9 layers RPC 8 layers for endcap The detector is hermetic for neutral and charged particle with excellent resolution, PID, and large coverage. NIM A614: ,

7 BESIII collaboration: 46 Institutes US (6) Univ. of Hawaii Univ. of Washington Carnegie Mellon Univ. Univ. of Minnesota Univ. of Rochester Univ. of Indiana Europe (9) Germany: Univ. of Bochum, Univ..of Giessen, GSI Russia: Dubna; BINP, Novosibirsk Italy: Univ. of Torino,Frascati Lab Netherland:KVI/Univ. of Groningen JINR Korea (1) Seoul Nat. Univ. ~ 300 collaborators Pakistan (1) China(29) Univ. of Punjab IHEP, CCAST, Shandong Univ., Univ. of Sci. and Tech. of China Zhejiang Univ., Huangshan Coll. Huazhong Normal Univ., Wuhan Univ. Zhengzhou Univ., Henan Normal Univ. Peking Univ., Tsinghua Univ., Zhongshan Univ.,Nankai Univ. Shanxi Univ., Sichuan Univ Hunan Univ., Liaoning Univ. Nanjing Univ., Nanjing Normal Univ. Guangxi Normal Univ., Guangxi Univ. Suzhou Univ., Hangzhou Normal Univ. Henan Sci. and Tech. Univ. Hong Kong Univ., Hong Kong Chinese Univ. 7 Japan (1) Tokyo Univ.

8 Physics Topics at BES Study of Light hadron spectroscopy search for non qq or non qqq states meson spectroscopy baryon spectroscopy arxiv: Study of the production and decay mechanisms of charmonium states: J/ψ, ψ(2s), η C (1S), χ C{0,1,2}, η C (2S), h C ( 1 P 1 ), ψ(3770), etc. New Charmonium states above open charm threshold. Precise measurement of R values, τ mass,... Precise measurement of CKM matrix Search for DDbar mixing, CP violation, etc. 8

9 BESIII commissioning o and data taking milestones Mar. 2008: first full cosmic ray event April 30, 2008: Move the BESIII to IP July 19, 2008: First e + e collision event in BESIII Nov. 2008: ~ 14M ψ(2s) events April il14, 2009: ~106M ψ(2s) events May 30, 2009: ~42 pb 1 at continuum (3.65 GeV) July 28, 2009: ~226M J/ψ events Aug. Dec., 2009: summer maintenance, SR run Jan June 2010: ~ 950 pb 1 at 3770 MeV June 2 15, 2010: scan at around 3770 MeV

10 Results from BESIII Confirm BESII results threshold enhancement in γpp, X(1835), New improved measurements h c, η c, χ cj,, New observations χ cj decays h c decays Light hadrons, ( ) J/ψ ψ(2s)

11 About h c ( 1 P 1 ) state tt The charmonium family has been studied for many years, the knowledge on h c ( 1 P 1 ) is still limited. c 1 The h c ( 1 P 1 ) state was observed by CLEO_c in c 1 E835 found evidence in pp h c γη c. For ψ(2s), only observed in ψ(2s) π 0 h c The main decay mode of h c : E1 transition h c γη c

12 h c at CLEOc (with whole data set)

13 h c at BESIII Inclusive analysis of ψ(2s) π 0 h c identify h c in the inclusive recoiling mass spectrum of π 0. E1 tagged analysis of ψ(2s) π 0 h c, h c γη c tag E1 photon (~503 MeV) in h c γη c h c significance improved in inclusive π 0 spectrum Exclusive analysis of ψ(2s) π 0 h c, h c γη c fully reconstruct the exclusive η c decays

14 Observation of h c : Inclusive ψ(2s) π 0 h c background subtracted Select inclusive π 0 A fit of D Gaussian signal + 4 th Poly. bkg Combined inclusive and E1 photon tagged tagged spectrum Br(ψ(2S) π 0 h c ) = (8.4 ± 1.3 ± 1.0) 10 4 (First measurement) Br(h c γη c ) = (54.3 ± 67± 6.7 ± 52)% 5.2) (First measurement) 14

15 Observation of h c : E1 tagged ψ(2s) π 0 h c,h c γη c BESIII PRL 104, (2010) background subtracted Select E1 photonto tag h c A fit of D Gaussian signal+ sideband M(h bkg. yield: 013± 018MeV/c 2 c ) = ± 0.13 ± 0.18 Γ(h c )= 0.73 ± 0.45 ± 0.28 MeV/c 2 (< 1.44 MeV/c 90% CL) (First measurement) Br(ψ(2S) π 0 h c ) Br(h c γη c ) = (4.58 ± 0.40 ± 0.50) 10 4

16 χ cj study at BESIII The χ cj decays provide good place to: study gluonium: χ c gg (qq)(qq) C. Amsler and F. E. Close,Phys. Rev. D 53, 295 (1996). test COM G. T. Bodwin et al., Phys Rev. Lett. D51, 1125 (1995). H. W. Huang and K. T. Chao, Phys. Rev. D54, 6850 (1996). J. Bolz et al., Eur. Phys. J. C 2, 705 (1998). Improved measurement of χ cj π 0 π 0, ηη, First measurement of χ cj ωφ First measurement of χ c1 ωω,, φφ χ c1 First measurement of χ cj γφ

17 Study of ψ(2s) γχ cj ; χ cj π 0 π 0, ηη (η, π 0 γγ ) ψ(2s) γπ 0 π 0 ψ(2s) γηη BESIII: PRD 81, (2010). χ c1 ππ, ηη not allowed by parity conservation. CLEOc: PRD 79, (2009). 17 Decay mode χ c0 (10 3 ) χ c2 (10 3 ) π 0 π 0 BESIII 3.23±0.03±0.23±0.14± ± ± 0.88±0.02±0.06±0.04± ± ± PDG ± ±0.08 CLEOc 2.94±0.07±0.32± ±0.03±0.07±0.04 ηη BESIII 3.44±0.10±0.24± ±0.04±0.05±0.03 PDG08 2.4±0.4 < 0.5 CLEOc 3.18±0.13±0.31± ±0.05±0.05±0.03 CLEOc used their own branching ratios for ψ γχ cj.

18 χ cj γv, V=φ,ρ,ω Events / ( 0.01 GeV/c 2 ) χ c1 γφ 140 χ c1 γρ 70 χ c1 γω BESIII preliminary Events / ( GeV/c BESIII preliminary Events / ( 0.01 GeV/c 2 2 ) ) BESIII preliminary M γ ω (GeV/c ) H M M γ ρ (GeV/c ) γ φ (GeV/c ) H B (10 6 ) BESIII CLEOc pqcd χ c0 γφ < 14.8 < χ c1 γφ 27.3 ± 5.5 stat < χ c2 γφ < 7.8 < χ c0 γρ 0 < 9.5 < χ c1 γρ ± 14 stat 243 ±19 ± χ c2 γρ 0 < 19.7 < χ c0 γω < 11.7 < χ c1 γω 73.5 ± stat 83 ±15 ± χ c2 γω < 5.8 < H χ c1 γφobserved first time. pqcd predictions too low. Difference may be explained by non perturbative QCD loop corrections. D.Y Chen et al, arxiv: v2. CLEOc: PRL 101, (2008) pqcd: Y.J. Gao et al., hep-ph/

19 Study of χ cj VV, V = ω,φ BR(10 3 ) χ c0 χ c2 φφ 0.94±0.21± ±0.30±0.25 ωω 2.29±0.58± ±0.47±0.36 BESII, PLB 642, 197 (2006) BESII, PLB 630, 7 (2005) χ c1 φφ(and ωω) should be highly suppressed because C parity requires L = 2. φφ χ c2 BESIII sees clear χ cj φφ 4K signals χ c0 χ BR(10 33 ) BESIII PDG08 c1 χ c0 φφ 0.80 ± ± 0.20 χ c1 φφ 0.42 ± 0.03 χ c2 φφ 1.15 ± ± 0.30 First observation of χ c1 φφ Errors: statistical only.

20 clear χ cj ωω 2(π + π π 0 ) ωω χ c 1 χ c 0 χ c 2 clear χ cj ωφ (π + π π 0 )(KK) χ c 0 χ c 1 ωφ χ c 2? First observation of χ c1 ωω. 20 Doubly OZI suppressed χ cj ωφ observed for the first time.

21 First observation of ψ(2s) γγj/ ψ Two photon transitions are well known in excitations of molecules, atomic hydrogen, and positronium. A. Quattropani etal, PRA 25, 3079 (1982). F. Bassani etal, PRL 39, 1070 (1977). A. Quattropani etal, PRL 50, 1258 (1983). CLEO observed two photon transitions in Υ(3S) Υ(2S). F. Butler etal, PRD 49, 40 (1994). Never been observed in the charmonium system. Observation helpful to understand QCD. Theoretically: potential models give discrete spectra (ψ(2s) (2S) γχ cj,χ cj γj/ ψ) ) coupled channel models can give continuous spectra. theoretical work ongoing. 21

22 select ψ(2s) γγj/ψ, J/ψ l + l - events. J/ψ ee channel (μμ similar): RM γ 2 γ 1 - high energy gamma, γ 2 - low energy gamma ee ee M γ1γ2 data background MC + continuum continuum only signal (phase space; BR = 1 x 10 - select events in box to enhance signal. see clear excess over BG + continuum in M J/ ψ distribution. Significance > 10σ B(ψ(2S) γγj/ψ) [both ee and μμ] = (1.02 ± ) x 10-3 ee BESIII preliminary 22 M J/ψ

23 pp mass threshold study at BES J / ψ γ pp BESII theoretical speculation: p p bound state (baryonium) FSI effect M pp -2m p (GeV) Observation of an anomalous enhancement near the threshold of p p mass spectrum PRL 91 (2003)

24 pp massspectrum spectrum inother channels The narrow threshold enhancement is not observed in those channels ϒ(1S ) γ pp@cleo J / ψ ω pp@besii ψ γ pp@ BESII M pp (GeV) No significant narrow strong enhancement near threshold (~2σ if fitted with X(1860)) 24

25 pp threshold CLEOc fit with one resonance as BES did: QWG2010 Z. Metreveli agree with BESII results CLEO-c preliminary fit with three contributions: BES considered these (2) and (3) as systematic errors. 25

26 pp mass spectrum and Dalitz plot at BESIII ψ(2s) ππ J/ψ, J/ψ γpp BESII J / ψ γ pp M 0. pp -2m 0. p (GeV) 2 3 M= MeV/c Γ < 30 MeV/c 2 (90% CL) M=1865±5MeV/c 2 Γ < 33 MeV/c 2 (90% CL) PRL 91 (2003)

27 J/ψ γpp BESIII preliminary BESII M= MeV/c Γ < 30 MeV/c 2 (90% CL) Fit result: Mass= ± 0.8 M ev / Γ< 8 MeV(90% CL) c 2 27

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29 X(1835) BESIII + + J / ψ γπ π η ( η γρ, ρ π π ) BESIII 18σ preliminary BESIII preliminary + + J / ψ γππηη ( ππη) BESIII preliminary i 9σ BESIII preliminary i

30 Mass spectrum fit??? BESIII preliminary Whether there are two new resonances, further careful study is needed. F it result(statisticsignificant~21 σ ) : M = ± 2.8( stat) MeV Γ= 99.2 ± 9.2( stat ) MeV BESII BESII result(statisticsignificant ~ 7.7 σ ) : M = ± 6.1( stat) ± 2.7( syst) MeV Γ= 67.7 ± 20.3(stat) ± 7.7(syst)MeV Hadron 09

31 Study of a 0 0( (980) f 0 0( (980) mixing from J/ψ φf 0 φa 0 φηπ χ c1 a 0 π f 0 π π π π Mixing intensity provides important information in understanding the nature of a 0 (980) and f 0 (980). Narrow peak (8 MeV) at around 980 MeV can be expected in ηπ (J/ψ φfφ φa φηπ case) or π + π a π 0 f π 0 0 φ 0 (χ c1 0 0 π + π π 0 case) invariant mass spectra.

32 ξ fa = Br(J/ψ φf 0 (980) φa 0 (980) φηπ 0 ) / Br(J/ψ φf 0 (980) φππ) = (0.6 ±0.2(stat.) t t)±0.2(sys.))% ))%(<11%@90%C 1.1% C. L) L.) ξ af = (0.32 ±0.16(stat.) ±0.12(sys.))% (< 90% C. L.)

33 Comparison of BESIII results with others

34 Summary BEPCII/BESIII upgrade completed successfully: Peak Luminosity of 3.2*10 32 achieved. ~106 M ψ(2s) and ~226 M J/ψ events obtained in ~950 pb 1 at ψ(3770) so far in Nice results are obtained More results will come soon

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